The invention deals generally with heat transfer apparatus which is based on change of state and evaporation/condensation systems such as heat pipes and vapor sources, and more specifically with a vapor source which automatically purges itself of any non-condensible gases which may exist in the vapor region.
There are several applications in which vapor devices are required to operate under conditions in which such devices are in a hydrogen atmosphere and subjected to intense heat. Heat pipe heat exchangers operating in hydrogen or flue gas environments are one, and nuclear propulsion systems for space are another. Under such conditions the hydrogen may permeate into the vapor device and affect its operation.
Nuclear propulsion systems which have been proposed for use in space involve a dual mode of operation. Such systems combine thermal propulsion and electric power generation in a single integrated unit. For propulsion, the nuclear reactor heats hydrogen within the core and exhausts it through a nozzle. At the same time, thermal energy from the reactor is converted to electricity by thermionic or other thermal to electric energy converters. Such thermal energy converters may be located either inside or outside the reactor core. The heat can be transferred to the thermal energy converters either directly from the heated hydrogen or from heat pipes which are in contact with the hot hydrogen and transfer the heat to more remote thermal energy converters.
Unfortunately, one of the characteristics of hydrogen is its ability to permeate through metal, particularly when the metal is at high temperature. This has caused problems in transferring reactor core heat to thermionic energy converters because the hydrogen present permeates directly into either the thermionic energy converters or the heat pipes which are used to transfer heat to the thermionic energy converters. When hydrogen enters either device the result is premature failure of the electrical generation system.
The thermionic energy converters fail because the hydrogen interferes with the thermionic process, even at very low hydrogen partial pressures of less than 100 Pascal. Alkali metal heat pipes are also appropriate for the temperatures developed within a nuclear reactor, but they will eventually stop operating because the hydrogen is swept to the condenser region and prevents access of the vapor to the condenser. Preliminary calculations indicate that most of the heat pipe condensers used in dual mode nuclear propulsion systems would be blocked after less than three hours of operation of the propulsion unit.